Search Google Appliance

Mathematical Charts and Tables

Conversion Tables

Conversion Tables

As has been suggested already, instructive mathematical charts introduced unfamiliar units of measure. A number of handy tables also were produced to assist in conversions. Perhaps the earliest such chart in the collections dates from about 1814, and is designed to convert from units divisible by twelfths to decimal units. The size of conversion factor and the way the numbers are written suggest that it was made to convert from Massachusetts pounds and shillings to U.S. currency. By the mid-20th century, the dollar prevailed throughout the United States, and Americans were more concerned with understanding foreign currencies when they traveled abroad. Toward that end, some purchased a slide chart called the UNICON, which allowed them to convert between dollars and numerous foreign currencies when they knew the exchange rate.

Engineers have long needed to perform conversions as part of their work. In the first half of the 20th century, manufacturers sometimes distributed small advertising cards that listed decimal equivalents of parts of an inch. Larger tables might list a large number of useful conversion factors. New efforts to introduce metric weights and measures in the United States in the 1970s led to the distribution of a range of cards and slide charts that eased conversions. These were distributed by organizations ranging from the federal government to a manufacturer of outdoor clothing and camping supplies to a producer of food emulsifiers and flavorings.

This Universal Currency Converter is a plastic-covered paper holder that contains a plastic-covered paper core. The user slides the core to match a foreign currency to the U.S. dollar, given a known exchange rate, and then reads off conversions for other amounts of U.S. currency. The table thus enables the user to avoid multiplication.

The back of the Unicon contains metric to common measure conversion tables for distances, liquid volumes, weights, temperature, time zones, and “unofficial” exchange rates, as well as a 6-inch and 15 cm ruler. These rates have some historical interest for nations that no longer exist, such as West Germany and the U.S.S.R.; for currencies that have been merged, such as that of various Eurpoean nations; and for changes in exchange rates. A sheet of instructions for the Unicon also has another table of weights and measures and a list of equivalent clothing sizes. The instrument and its instructions are stored in a plastic case, meant to be carried in the pocket of travelers.

This example of the Unicon was given to the Museum by one of its inventors, David J. Schlink (1931–2010). Schlink and Walter K. Schwarz received U.S.Patent No. 3,680,775 on 1 August 1972 for the Unicon. They assigned the patent to Schlink’s employer, The Peoria Journal Star, Inc., of Peoria, Illinois. Under the name PJS Enterprises, the newspaper manufactured and sold the Unicon for $3.95 retail. Distribution soon was taken over by Unicon Enterprises of Peoria, which sold a later version of the instrument, the Unicon II, as late as 1988. By this time, foreign travelers also were advised to take along electronic calculators for currency conversion.

Schlink wrote two books on currency conversion, Money Sense Overseas (or,Unicon I), which sold in 1984 for $4.50 (ISBN 0912327006) and Unicon II, which sold in 1983 for $4.95 (ISBN 0912327014). It is not clear why Unicon II was copyrighted before Unicon I.